1. Field of the Invention
This invention relates to a variable air induction control system for an internal combustion engine, more particularly to a variable air induction control system for an internal combustion engine which is equipped with a main air intake passage and an auxiliary air intake passage provided with an air flow rate control valve and the amount of intake air supplied to the engine is variably controlled in response to at least one engine operating condition of the engine.
2. Description of the Prior Art
In an internal combustion engine which is equipped with a main intake passage and an auxiliary intake passage and with an air flow rate control valve in the auxiliary intake passage which is opened and closed in response to at least one engine operating condition, it is known to control the operation of the engine by, for example, controlling the ignition timing thereof. A system for carrying out such control is disclosed, for instance, in Japanese Laid-open Patent Application No. 58(1983)-48776.
In connection with the air intake characteristics of an internal combustion engine, it is known that the region providing maximum engine output is determined mainly by the length and diameter of the air intake passage. Thus, when an air intake system is designed with primary attention given to performance in the low engine speed operating region, the air intake characteristics become poor in the high engine speed operating region. Conversely, when priority is given to the high engine speed operating region, the air intake characteristics in the low engine speed operating region will suffer. Thus, to realize improved air induction efficiency (charging efficiency) in both the high and low engine speed operating regions, there was developed the aforesaid system having main and auxiliary air intake passages and an air flow control valve in the auxiliary air intake passage which is opened and closed in response to one or more engine operating conditions such as the engine speed and the degree of throttle valve opening.
In this prior art system, in order to improve engine output ignition timing is controlled in response with the opening and closing of the valve in the auxiliary intake passage as well as on the main engine operating conditions including engine speed and engine load. However, such a control system is still insufficient and indirect for maximizing the engine output, since it disadvantageously becomes necessary to carry out an additional operation to compensate the ignition timing for other engine operating conditions as well as for such environmental conditions as the intake air temperature and the coolant temperature.
Also, while it is possible to realize increased engine output by variably controlling the flow rate of air supplied to an internal combustion engine so as to improve air induction efficiency, such control is unfortunately accompanied by increased risk of knocking. The aforesaid prior art system, in fact, leaves much to be desired with regard to regards knock prevention.